don't fuck with that treadmill shit, its boring and you'll end up lookin like these kenyan distance runners.

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Thats not completely true, it's very subjective, I personally have a lcd in front of my tread, along with an mp3 player and I like it. I personally also like certain ellyptical machines.

It really depends on your goal and your frequency / volume / intensity. In this guys case, it might very well end up making him look like a long distance running (skinny / soft).

You're only going to start losing muscle when you go for long periods of time / aerobic/performance speeds and do it consistently with a lifting schedule because you'll start to burn protein for energy. Either way, if you up your caloric intake to match your cardio, you can help avoid this. This wouldn't be great for dude because he's not looking to really "gain". But I digress.

It's a known fact that many bodybuilders during cutting phases will walk for 45-1hour at around 3mph in multiple weekly sessions because it uses fat as a secondary energy source instead of carbs after about 15 mins, which fluctuates with each person. This method helps retain muscle. In fact, walking in general dependant on speed can be quite beneficial. It may not seem like it because you're used to working up a big sweat or what not.

If you do moderate cardio a couple times a week for 30-45 mins during a gain/ bulk phase you don't lose muscle. I can attest to this while still doing a 4 day split.

High Intensity Interval Training (HIIT), for tightening up and losing some weight this is supposed to be the best method.

So with that being said, I would say the boxing methods described would probably work for you to meet your goals, but it's not the ONLY way to go about it.